Combinations of the colorants cyan, magenta, and yellow (CMY) are capable of producing images containing colors in the visible spectrum, so many color imaging systems are designed around CMY colorants. To improve image quality and to reduce the costs of printing, black is sometimes added to a CMY color gamut to form a CMYK (cyan, magenta, yellow, and black) color gamut. The visual details of an image rendered from a CMYK color gamut are sharper than the visual details of the same image rendered from a CMY color gamut. Similarly, the gray balance of an image rendered from a CMYK color gamut is better than the gray balance of an image rendered from a CMY color gamut. So, many modern color imaging systems utilize the colorants cyan, magenta, yellow, and black (CMYK) in forming color images.
Most conversion methods from CMY to CMYK simultaneously add black colorant and reduce the amounts of cyan, magenta, and yellow. One popular solution is based on a combination of Under Color Removal (UCR) and Black Generation (BG) functions:PK=min(C,M,Y) C1=C−UCR(PK) M1=M−UCR(PK) Y1=Y−UCR(PK) K1=BG(PK)  (1) where (C, M, Y) are input values and (C1, M1, Y1, K1) are the output values. The black generation function computes the black colorant amount based on the process black amount P. The CMY values are reduced by an amount dependent on PK. However, such a simple transformation does not preserve colorimetric relations and does not allow use of the whole printer gamut.
Unfortunately, even though each of these processes show improved gray balance in images rendered from a CMYK color space when compared with images rendered from a CMY color space, each of these processes also has some disadvantages. One disadvantage is that the UCR and GCR processes are not based on human visual perception and therefore fail to faithfully reproduce the original image. A second disadvantage of most CMYK systems is that they fail to utilize the entire gamut of the CMYK color space. Failing to utilize the entire gamut results in a suboptimal rendering of a CMY image in a CMYK color space.
For these and other reasons there is a need for the present invention.